This invention relates to belt or chain drive systems, and relates in particular to a method and apparatus for setting the proper tension in belt and chain drives.
A common usage of such a belt or chain drive system would be in the automative industry wherein power is inputted into the system by the engine and various accessories are driven by an endless or serpentine belt. However, such a system is illustrative only and the principles of the invention described herein need not be limited to the endless type system.
Setting the proper tension in such belt drives is a continuing problems which becomes more severe as user demands for lower cost, less space, more power, higher reliability and fewer skills in assembly become more stringent. Furthermore, many common adjusting techniques lack accuracy and require iterations which lead to abandonment of the effort before precise tensioning is achieved.
A number of specific problems are encountered in the operation of systems of this nature and proper tension in the face of these problems is important. For example, often the input power is not smooth, but pulsates. Additionally, the load demands of the individual components such as, for example, an air conditioning compressor may be high and pulsating, or from other components such as, for example, a power steering pump or alternator may be high and intermittent or, for example, such as an air pump may be low and constant. Various combinations of these variables can also be encountered.
When a belt is kept at the proper tension, which may vary with the length of the belt, its product life is increased, and the cost of maintenance and repairs is greatly reduced. For example, excessive friction results if the belt is tensioned too tightly, and slippage or whipping results if the belt is tensioned too loosely. Both conditions shorten the life of the belt, and often one leads to the other, i.e., a loose belt which exhibits whipping is often remedied by over tightening which results in power loss due to excessive friction.
In general practice, the tension of a belt is measured by utilization of a belt tension scale. The scale is placed on the belt itself, a force is applied to the belt by the scale, and a reading of the tension is obtained. This commonly used method may actually deleteriously deform the belt as the belt is bent or stretched during the process. Additionally, the accuracy of the measurement is questionable as a secondary tension is applied in reading the belt tension.
Belts such as are involved herein are thus difficult to tension correctly at the time of manufacture and initial assembly, and are even more difficult to tension correctly after being placed n service. Unfortunately, in view of the need for longer product life and increasingly stringent product liability requirements, these difficulties assume fairly major dimensions.